Lung Alveolus Structure – Lung Alveoli Anatomy

A magnified view of an alveolar sac

About 95% of the alveolar surface consists of simple squamous epithelial type I cells, and the remaining 5% is occupied by type II cells (or septal cells).

1

2

3

These large, rounded cells are located between the type I cells andsecrete the pulmonary surfactant. The complex of phospholipids and proteins in the surfactant reduces surface tension inside the alveoli, which keeps the alveolar walls from sticking together as they deflate during exhalation.

Small openings called alveolar pores perforate the interalveolar wall and allow air to pass between alveoli. They provide alternative routes to and from the alveoli if an obstruction occurs.

1

2

A network of capillaries and many supportive collagen and elastic fibers are found in the narrow interstitial spaces that separate the alveoli.

1

2

Numerous macrophages (or dust cells) protect the lungs from damage. click here to see a histological demonstration of the alveoli

1

2

3

Macrophages (dust cells) move about the air spaces and between the alveoli, where they remove (engulf) inhaled particles, foreign invaders, and other types of harmful substances.